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TITLE: Cancer peril of animal organ transplants
SOURCE: The Observer, UK, by Robin McKie
DATE: July 23, 2000
-------------------- archive: http://www.gene.ch/ --------------------
Cancer peril of animal organ transplants
Transplanting animal organs into humans could trigger a global
pandemic of a deadly new disease. A new study by British scientists
has found that cancer-causing retroviruses are spread relatively
easily between different creatures in the wild. The discovery,
outlined last week by the Natural Environment Research Council, will
reinforce concerns raised by experiments which recently revealed that
pig hearts and kidneys carry potentially deadly animal retroviruses,
dashing hopes that animals could one day supply spare parts for human
surgery.
As a result of these initial experiments, Western health authorities
imposed a moratorium on all xenotransplant surgery, although
biotechnology companies are known to be continuing with research.
Human organs are desperately scarce, as are supplies of brain tissue
for treating stroke victims and Parkinson's sufferers. It was hoped
specially-reared animals, mainly pigs, would provide tissue and
organs for tens of thousands of operations a year.
The dangers of this plan are underlined in the study by biologists
Michael Tristem and Joanne Martin of Imperial College, London, which
focused on murine leukaemia viruses, close relatives of the cancer
retroviruses that are known to infect pigs. Traces of virus DNA were
found in a range of mammalian species in the wild, suggesting that
pig retroviruses are capable of infecting other animals - including
humans - with relative ease.
'There are two ways to demonstrate that animal retroviruses pose
risks,' said Tristem. 'You can show they can be grown in human cells
in the laboratory. Scientists have done that. Or you can show such
viruses jump easily between species in the wild. Our study now proves
this also happens - that cancer viruses will jump species in the real
world, not just in artificial laboratory settings.'
Finding leukaemia virus DNA mixed up with the genes of different
animals does not prove these creatures were all made ill by their
infection, Tristem admitted. 'However, when viruses jump species they
usually acquire pathogenic properties, just as HIV did when it leapt
from monkeys to humans. There is a real, but small risk that pig
organ transplants could trigger a new disease epidemic.'
Virologist Professor Robin Weiss, who first demonstrated that pig
viruses could infect human cells, agreed. 'Xenotransplants do not
seem to pose a big risk. But then BSE or HIV were not thought to pose
big risks when they were first discovered. We obviously have to be
very careful.'
Professor George Griffen, a member of the UK Xenotransplantation
Interim Regulatory Authority, said: 'There is always going to be a
chance that a viral stowaway could be transplanted into a human along
with a pig heart or kidney. It could then spread through his or her
body, and then to other individuals, triggering a new epidemic.
'However, if the risk of this happening is found to be very, very
small, would it be right to block xenotransplants, given that they
could help treat so many serious illnesses? And don't forget that
none of the hundreds of pre-moratorium xenotransplant recipients have
yet to show reactions to retroviruses.'
Sceptics point out that transferred viruses could take decades to
take effect, and these transplant patients could still develop
retroviral illnesses in 20 years. They also argue that stem cell
surgery, in which the patients' own cells are used to grow new
organs, could soon obviate the need to use animal hearts or livers.
'I think it is now touch and go whether xenotransplants will ever be
given the go-ahead in the West,' said Griffen.
Even if they were approved, operations would only be permitted under
the most stringent conditions. Patients would have to be monitored
and tested for the rest of their lives, as would their sexual
partners and children.
What worries some researchers is the prospect that these costly
lifetime safeguards may drive an unscrupulous surgeon or biotech
company to carry out transplants in 'xeno-havens', developing nations
that do not impose regulations.
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